Certain examples would suggest Aristotle’s idea of gravity to be true, such as dropping an rock and a leaf at the same time. The rock will fall to the ground faster. However, Italian scientist Galileo had his suspicions about the veracity of this experiment and decided to put it to the test. He experimented by rolling balls of different masses down sloped planes and found that it was possible to have two balls of different masses reach the bottom of the plane at the same time. This discovery suggested that the rate of acceleration to the earth is universal, a novel concept that contradicted Aristotle’s theory of gravity.
Physicist Isaac Newton built off of this idea, shortly after Galileo, and made a great leap in the theory. He made a proposition in 1687 that had tremendous success in predicting the strength of gravity. Isaac believed that the force of gravity that causes a ball thrown into the air to retreat back to the earth was the same force that caused the planets to orbit around the sun. His Law of Universal Gravitation says that a particle attracts every other particle in the universe. The degree of this attraction is proportional to the product of their masses and is inversely proportional to the square of the distance between their centers. It took another 250 years before this a new theory showed this one to be incorrect, and this is because for most practical purposes this theory is “correct.” Newtonian gravity, in combination with Newtonian motion, explains the orbit of the planets around the sun, the orbits of the moons around the planets, gravity as we see experience it here on earth, and the ocean tides. Whenever astronomical measurements seemed to be in discordance with Newtonian gravity, it was ultimately found that the measurements were for some reason incorrect. One example is the course of Uranus rotating about the sun. Measurements of it’s orbit appeared to violate Newtonian gravity. However, scientists speculated that some undiscovered planet could possibly be pulling on Uranus and altering it’s orbit and a man named U.J.J. Le Verrier decided to put this theory to the test and calculated where this mysterious planet may be based on Newton’s laws of gravity and motion. When he trained his telescope to aim at that spot, there the planet (Neptune) was, exactly where Newton’s Laws said it should be.
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